Sn-Ag-Cu系錫球材料被廣泛應用在電子構裝技術。作為電流訊號傳輸的橋樑，高電流通量可能導致銲點的失效。又Sn-Ag-Cu系錫球在射球或迴銲過程中表面會有顏色改變的現象。因此銲錫材料的熔斷電流和凝固表面皮膜組織的特性需要深入的研究。

　　本研究選擇Sn-3.5Ag-xCu (x = 0、0.5、1.2、1.9、2.2) 合金為實驗材料。研究分兩大主題，首先探討Cu含量和凝固速率對於Sn-3.5Ag-xCu合金微觀組織與通電性質之影響。接著則對於不同成分 (pure Sn、Sn-3.5Ag、Sn-3.5Ag-2.2Cu) 和不同凝固速率的凝固表面皮膜進行一系列的分析。

　　實驗結果顯示，隨著Cu含量增加，微觀組織中Cu6Sn5的晶出量增加。當Cu含量超過1.2wt%之後，微觀組織出現β-Sn樹枝狀晶明顯微細化及共晶區面積上升的現象，試料的熔斷電流和電導度下降。當凝固速率變慢後，Sn-3.5Ag合金中的Ag3Sn變為長條狀，試料的熔斷電流和電導度上升；Sn-3.5Ag-2.2Cu合金中的Cu6Sn5成長，試料的熔斷電流和電導度幾乎不變。

　　凝固表面皮膜的分析結果顯示，表面產生顏色變化的試料，表面氧化生成由SnO和SnO2所組成的皮膜，TEM觀察到的皮膜厚度約為0.5μm。在同樣的凝固速率下，純Sn和Sn-3.5Ag試料表面氧化的程度相近，Sn-3.5Ag-2.2Cu試料表面氧化的程度較輕微。隨著凝固速率變得更緩慢，表面氧化的時間增加，表面顏色變深，但皮膜中Sn的化學態變化不大。

　　Sn-Ag-Cu solder balls are extensively applied in the electronic packaging technique. Because the solder balls are used to transmit current, high current density may induce the failure of solder joints. In addition, the surfaces of Sn-Ag-Cu solder balls discolor at injected or reflowed processes, so the fusion current and the solidification scale of solders need to be investigated.

　　Sn-3.5Ag-xCu (x = 0、0.5、1.2、1.9、2.2) solders are specimens of the study. The subject of the study divides into two parts. The first part is the effect of Cu content and solidification rate on the microstructure and electric properties. The second part is analyses of the scales with different components (pure Sn, Sn-3.5Ag, and Sn-3.5Ag-2.2Cu) and different solidification rate.

　　Experimental results show that the Cu6Sn5 content increases with the increasing of Cu content. By adding more than 1.2wt% Cu, the β-Sn dendrites become refined apparently, and the eutectic area increases. It also causes the decrease of fusion current and conductivity. When solders solidify at the slower cooling rate, the features of Ag3Sn in Sn-3.5Ag solders become rod-like. It also causes the increase of fusion current and conductivity. Cu6Sn5 compounds in Sn-3.5Ag-2.2Cu solders expand, but fusion current and conductivity have no obvious change at the slower solidification rate.

　　The analysis show that oxidization occurs on the surface of discolored specimens and the scales are composed of SnO and SnO2. According to TEM analysis, the depth of scale is ~ 0.5μm. At the same solidification rate, the extent of oxidization on pure Sn is similar to that on Sn-3.5Ag solders. However, the extent of oxidization on Sn-3.5Ag-2.2Cu solders is slightly less. The surface color of solders becomes darker at slower solidification rate, while the chemical state of Sn does not change obviously.

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